Magnetic Fields and Electromagnetic Induction The Earth’s Shield Magnetic Fields and Electromagnetic Induction

Electromagnetic Induction All charges produce ELECTRIC FIELDS Moving charges produce MAGNETIC FIELDS PERPENDICULAR to the motion of the charge Magnetic field lines

Making a Magnet Magnetism is a FIELD FORCE No contact required All atoms have “some” natural of magnetism Three strongly magnetic elements IRON, NICKEL, COBALT

Electromagnetic Induction Magnets produce magnetic fields Moving magnets produce ELECTRIC FIELDS PERPENDICULAR to motion of the magnet This causes ELECTRICAL CURRENT to flow

Magnetic Field Lines Rules for field line directions Outside magnet  NORTH TO SOUTH Inside magnet  SOUTH TO NORTH

Magnetic Field Maps N S

Magnetic Field Maps S N N S

Magnetic Field Maps S N

Field is strongest at point C. Example #1 Determine the direction of the magnetic field lines at each point. Where is the field strongest? A Field is strongest at point C. N S B C D

Field is strongest at point F. Example #2 Determine the direction of the magnetic field lines at each point. Where is the field strongest? H E S N N S F G Field is strongest at point F.

Compass The needle of a compass is a small MAGNET The north pole of a compass needle … is marked with a small “N” or a prominent color … points toward magnetic SOUTH poles.

Example #3 Determine the direction in which the compass will point. S N

Like poles REPEL. Unlike poles ATTRACT.

Could you separate the poles of a bar magnet by breaking it in half Could you separate the poles of a bar magnet by breaking it in half? Why? No, if you break a magnet in half, you create two smaller magnets, but each still has two poles.

Permanent (Hard) magnet - a material that retains its magnetic properties after an external magnetic field is removed.

Temporary (Soft) magnet - A material that shows magnetic properties only while exposed to an external magnetic field.

Electromagnet - A coil of wire wound about a magnetic material, such as iron, that produces a magnetic field when current flows through the wire.

Polarization - the temporary alignment of the magnetic domains in a magnetic material when it is placed near a magnet.

Polarization - the temporary alignment of the magnetic domains in a magnetic material when it is placed near a magnet.

Magnetic flux (B) – a vector quantity representing the number of magnetic field lines that pass through a given area. The magnetic field is strongest where the lines are closest together. (most concentrated at poles) Unit - Tesla (T) = kg / s2•A

In Across Out

Which picture has a greater magnetic field intensity (magnetic flux)?

Earth’s Magnetic Field The geographic NORTH pole of the Earth acts like the SOUTH pole of a magnet! Convection currents in the outer iron core produce the Earth’s magnetic field

The Magnetosphere

End of 4.3.1 – PRACTICE